Influence of Ceria and Nickel Addition to Alumina-Supported Rhodium Catalyst for Propane Steam Reforming at Low Temperatures

Open Access
Author:
Li, Yan
Graduate Program:
Energy and Geo-Environmental Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 28, 2009
Committee Members:
  • Chunshan Song, Dissertation Advisor
  • Chunshan Song, Committee Chair
  • Andre Louis Boehman, Committee Member
  • Chao Yang Wang, Committee Member
  • Kwadwo Osseo Asare, Committee Member
Keywords:
  • Propane
  • Steam reforming
  • Nickel
  • Ceria
  • Alumina
  • Rhodium
  • Catalyst
  • Kinetics
Abstract:
This work aims to develop a fundamental understanding of the catalyst composition-structure-activity relationships for propane steam reforming over supported Rh catalysts. The work investigates the influence of ceria and nickel additions to alumina-supported Rh catalysts for propane steam reforming at low temperatures using different loading levels for ceria and Ni. An optimum loading is found in terms of reforming activity. In this work, 2 wt% Rh and 5 wt% Ni supported on 20 wt% ceria modified alumina exhibits the highest activity. TPR characterization shows ceria and nickel loading can change both the metal-metal and metal-support interactions. Generally, adding ceria makes rhodium oxide easier to reduce, and the presence of rhodium makes ceria easier to reduce, whereas the addition of nickel makes rhodium oxide more difficult to reduce. FE-SEM and XPS results indicate that ceria is highly dispersed on alumina surfaces with ceria loading of less than 20 wt%. Adjusting ceria and nickel loading can change the nanostructures of catalytically active phases, thus influencing the propane reforming rate of Rh catalysts at low temperatures. A kinetic study at different temperatures (450 - 650 °C) indicates that adding ceria and nickel can greatly increase the propane reforming rates by lowering the activation energies. A kinetic equation based on the Langmuir-Hinshelwood model was applied to Rh-based catalysts. Results at different partial pressures of propane and steam reveal the addition of ceria can enhance steam and propane adsorption, while the addition of Ni can promote propane adsorption, probably through working with Rh as propane adsorption sites. The kinetic study shows the importance of a balance between steam and propane adsorption. Possible active phases on the catalysts are also discussed.